We have had serious issues with rsync reporting "unexpected tag 3 [sender]" since upgrading to 2.6.8. I applied the patch described in:
http://www.mail-archive.com/rsync@lists.samba.org/msg16205.html
... but now we get this error message just uploading (push upload to rsync server) from 2.6.8-patched to 2.6.8-patched!

Use the updated version of the patch from the reply to the message you cited:
http://www.mail-archive.com/rsync@lists.samba.org/msg16405.html
That's the official fix that is now in CVS. The tag-3 error is not possible with that patch. (Feel free to try out the CVS version, perhaps using one of the nightly tar files as an easy way to grab the source.)